Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

purpose of this campaign was to gather information on the occurrence of surface earthquakes related to the activity of the Puerto Aldea Fault and adjacent structures. The seismic stations collected seismic and microseismic data for 7 months, retrieved between February 22 and 24, 2023. The analysis of seismological data, which involves identifying the arrival times of P and S waves from local earthquakes at seismological stations, was conducted automatically using a program based on neural networks (Machine Learning). This method has been used with good results for earthquake localization (Kong et al., 2018), especially for earthquakes generated in intraplate faults such as the San Ramón Fault (Ammirati et al., 2019). This method, already tested in Chile (Pastén-Araya et al., 2022), yields excellent results when the artificial intelligence is trained with representative local data regarding noise level or, for example, regional seismicity rate. Thus, we conducted specific training based on a manually processed sample of local earthquakes to ensure the dataset's quality. This approach includes the geological interpretation of seismic profiles (acquired), which delineate the submarine extension of the fault into Tongoy Bay; the mapping of geomorphological features, faults, and geological units using satellite imagery, supported by drone technology; developing three-dimensional structural models of active faults identified at depth; and creating seismic ground acceleration models. Based on the results, a comprehensive assessment of the seismic hazard posed by the Puerto Aldea Fault will be carried out. This could have significant implications for the seismic response of urban infrastructures along the coast between La Serena and Tongoy, particularly under worst- case scenarios. R E S U LT S / D I S C U S S I O N Recentmicroseismicdataprovidedbya local temporal network (Figure 1), which was operating for 7 months, show that upper crustal microseismicity occurs in the study area (<25 km depth). Based on a preliminary analysis of seismic data (considering 5 random days: 08/08/2022, 24/09/2022, 24/10/2022, 28/11/2022, and 08/01/2023), an average of ~30 events/day were obtained, with a projection of ~6500 events over a total of 218 days. From this seismic data, several events occurring in the upper crust were identified. This was determined from the existing relationship between the distance from the seismological station to the event's hypocenter and the arrival time of the S and P waves. Of the recorded events, a significant proportion of earthquakes are located offshore. To achieve better resolution of these earthquakes, additional working time was required to accurately locate them. Using the BATHY 2010 sub-bottom profiler (SyQwest), 30 seismic profiles were obtained in Tongoy Bay. Preliminary, the obtained profiles show that there would be a submarine extension to the north of the Puerto Aldea Fault of at least 8 km (Fig. 1). These profiles will be interpreted by characterizing the different seismostratigraphic units present, as well as the characterization of submarine geomorphological features and deformation of the seabed substrate associated with the Quaternary activity of this fault (Fig. 1b). Therefore, these data will be essential to complement the information obtained in the subaerial part of the study area. Previous identification, using high-resolution satellite images (Alos Palsar 12.5x12.5 m), of several tectonic geomorphologic and structural features present in the study area have been verified through direct observation during two field trip campaigns.